1. Field of the Invention
The present invention relates to an electrically heated catalyst device and its manufacturing method.
2. Description of Related Art
In recent years, EHC (electrically heated catalyst) devices have been attracting attention as an exhaust purification device that purifies exhaust gases discharged from engines of automobiles and the like. In EHC devices, it is possible to enhance the purification efficiency of the exhaust gas by electrically heating and forcibly activating a catalyst even under such conditions that the temperature of the exhaust gas is low and thus the catalyst cannot be easily activated, such as immediately after the engine is started. It should be noted that unburned HC (hydrocarbon), CO (carbon monoxide), NOx (nitrogen oxide) and so on contained in an exhaust gas are removed by the catalytic reaction.
Japanese Unexamined Patent Application Publication No. 2013-136997 discloses an EHC device in which on the outer surface of a cylindrical catalyst support that has a honeycomb structure and supports a catalyst such as platinum and palladium, a pair of surface electrodes extending in the axial direction of the catalyst support are disposed opposite to each other. A plurality of comb teeth-like wiring lines extending in the circumferential direction are connected to each of the surface electrodes and a current is supplied to the surface electrode through the comb teeth-like wiring lines.
Since the EHC device is disposed on an exhaust path of an automobile or the like, the above-described surface electrodes and wiring lines are composed of metallic material having excellent heat resistance, oxidation resistance at a high temperature, corrosion resistance in an exhaust-gas atmosphere and so on as well as excellent electrical conductivity. Meanwhile, as for the material for the above-described catalyst support, ceramic material such as SiC (silicon carbide) is used. As a result, when the EHC device is electrically heated, a thermal stress occurs due to the difference between the linear expansion coefficient of the metallic material forming the surface electrodes and wiring lines and that of the ceramic material forming the catalyst support.
In an EHC device disclosed in in FIGS. 1 and 2 of Japanese Unexamined Patent Application Publication No. 2013-136997, each of the comb teeth-like wiring lines is fixed to a surface electrode by using a button-like fixing layer so that the thermal stress is reduced. Further, since the comb teeth-like wiring lines are arranged in parallel with each other from one end of the surface electrode to the other end in the axial direction of the catalyst support, the current spreads in the axial direction of the catalyst support in the surface electrode and thus the entire catalyst support can be heated.